Method of determining location of liquid level in wells



Patented May 19, 1942 2,283,477- Mn'rnon or DETERMINING LooATioN F mourn LEVEL m WELLS 'Cranford P. Walker, San Marino, Calif.

Original application October 26, 1937, Serial No. 1

1939, Serial No. 268,806

6 Claims.

My invention relates to methods and apparatus for determining the location of the liquid level in deep wells such as ofl wells and the like, and has particular reference to methods and apparatus which may be readily and economically employed upon wells having a mechanical pump therein to determine when the liquid level is at or immediately adjacent to the inlet of such pump.

This application is a division of my copending application Serial No. 171,170, filed October 26, 1937, wherein is described and claimed methods of determining the density of the liquid in the standing column about the pump and pump tubing for determining the pressure existing in the standing column at any point below the normal liquid level and for determining the maximum production capacity of a well all of which methods utilize the measurement of the location of the liquid level in the-well. I

It is the common practice in oil well production activity to permit an oil well to produce as a flowing well, that is, to permit the oil to flow out at the ground surface due to the pressure in the oil formations, until the production rate reaches a considerably low value or ceases, after which gas lifting is usually attempted and continued until the production rate with gas lifting reaches a relatively low value or the production entirely ceases. At this time, and in some instances prior to any attempt to gas lift the oil, mechanical pumping devices are usually installed to lift the oil by mechanical means to the surface, these pumps usually comprising a pump barrel located at a considerable depth in the well, usually 50 to 150 feet below the surface of the liquid in the well while it is producing, plungers or other reciprocating devices being employed in the barrel and operated from the ground surface by means of sucker rods.

Usually the selection of the size and character of the pumping equipment is determined by the production of the well during its flowing or gas lifting life by estimating from this production the type or character of pump which appears to be most suitable. In many fields, however, the type, size and character of the pump installed is usually one determined as standard for that particular type of well in the particular'fleld. In other words, it is one having the same dimensions as pumps in other wells producing from the same horizon. Frequently, such well receives no further attention until the field as a whole has declined to a point where it becomes necessary to increase the production from the wells, as for Divided and this application April 19,

example, by the encroachment of water, necessitating the lifting of greater quantities of fluid in order to obtain the desired amount of oil. When this condition occurs, it is customary to increase the capacity of the pumping equipment.

For example, if the pumps in the particular field are operating at good volumetric efiiciency, much can be determined from the quantity of oil produced and the volumetric displacement per stroke of the pump, and if the pumps are operating at their maximum capacity, the fact that the fluid level is at a considerable distance above the pump inlet may indicate that the operator is justified in making a change in the size or character of the pumping equipment. Again, if the volumetric 'efiiciency of the pump is found to be low, as for example, when the pump appears to be taking in a comparatively large quantity of gas upon each stroke of the pump, the operator should know whether or not the inlet of the pump is located at a point too near the liquid surface so that he may determine how far below the liquid surface he should lower the pump in order to allow it to receive liquid for the full stroke.

To determine the correct location of the pump, it is desirable to know the normal pressure at the pump inlet when the pump is producing oil from the well and this determination may be made in many wells by moving the liquid surface to a position so close to the pump inlet that the pump will take in free gas upon eachcycle of its operation. The entry of free gas into the pump will produce pressure waves within the gas column or annular space between the pump tubing and the casing .of the well, which pressure waves will travel to the ground surface and there may be detected by suitable pressure responsive mechanism such as is illustrated and described in my copending application Serial No. 164,534, filed September 18, 1937, and in United States Letters Patent No. 2,156,519, issued to me on May 2, 1939.

By properly observing or recording 1 these pressure waves at the ground surface, they may be readily distinguished from other pressure waves or disturbances in the gas column resulting from other causes. Hence by observing the sound waves or pressure waves produced atv the pump, the fact that the fluid level is at or immediately adjacent to the pump inlet may be determined. The information so obtained may be utilized in accordance with the methods for determining pressure and production capacity described and claimed in my copending application Serial No. 171,170 hereinbefore referred to.

provide a method for determining whether or not the liquid level is at or adjacent to theinlet of the pump by observing the peculiarly distinguishable pressure waves set up as a result of the inflow of gas into the pump, provided there is considerable pressure in the casing of the well. Another object of my invention is to provide a method and apparatus for so observing the pressure waves or sound waves resulting from inflow of gas into the pump when the level of the liquid is at or adJacent to the pump that this condition may be distinguished from sounds or pressure waves resulting from other causes.

Other objects and advantages of my invention will be apparent from a study of the following specifications, read in connection with the accompanyins drawing, wherein Fig. l is a diagrammatic cross sectional view of a typical oil well illustrating the manner in which the location of the liquid surface at the pump inlet may be detected; and

Fig. 2 is a diagrammatic view illustrating the type of record produced by the pressure wavesor sound created when the fluid level is at or admcent to the pump inlet and which may be recorded by the recording apparatus illustrated in Fi 1.

teferring to the drawing, I have illustrated in Fig. 1 a typical oil well which includes a casing I extending down through the well bore from the ground surface 2 into the oil producing sands, the oil flowing from the sands or oil formation into the casing and rising in the casing to some level indicated at 3. Pumping apparatus employed to remove the oil from the well usually includes a suitable pump 4 located upon tubing string 5,- constituting the flow tubing through which the oil is raised to the ground surface, the pump 4 including usually some reciprocating mechanism operated by reciprocal movements of a string of sucker rods Ii extending down through the tubing 5 and connected to reciprocating power apparatus at the ground surface, as indicated at I. The flow tubing 5 is provided with an outlet 8 communicating with a suitable oil line through which the oil pumped from the well is conveyed to any desired location.

The casing I is closed at its upper end as indicated at 9, an outlet Ill being provided communicating with the casing I to permit gas escaping from the oil to pass into a suitable gas line II, a control valve I2 being usually provided to control the flow of gas into the gas line.

As will be understood by those skilled in the art, the oil which flows from the formation into the well may be substantially free of gas or may contain relatively large quantities of gas entrained with the liquid so that the pressure of the oil and gas mixture within the well, and particularly in the standing column of liquid in the annular space between the pump tubing and the casing, will vary through relatively wide limits. However, if the pressure existing in the oil and gas mixture can be determined or calculated for any desired point therein below the normal liquid level, this information may be readily 'used to determine the best location for the pump to insure its maximum volumetric efliciency; that is, since the pump is operating upon a liquid and gas mixture, it is desirable that the pump should be located at the level within the liquid column at which the maximum separation of gas from the mixtu're occurs else upon each stroke of the pump the pump will take in relatively large quantities of gas which will expand within the pump and seriously reduce its volumetric efficiency. If, however, the pump is properly located in the ofl and gas mixture column, at which the gas readily separates from the liquid and bubbles out as free gas to pass up through the casing, the pump will be operating upon relatively dense fluid.

To assist in the determination of the correct location of the pump, the pressure existing at the pump inlet should be known. As is explained in myapplication Serial No. 171,170, the pressure to maintain the liquid level at some known location.

For example, it may be assumed that the height to whichthe standing column of liquid will rise in the well will be such that the pressure in the formation which causes the oil to flow into the well is just balanced by the height of the liquid column, plus the gas pressure which exists at the casing head of the well, plus the eifect in pressure of the column of gas between the liquid surface and the casing head. If the location of the liquid level is known, it follows that by merely measuring the casing head pressure, multiplying the number of feet of gas column existing between the liquid surface and the casing head by the unit weight per foot of the gas, and adding the product so found to the casing head pressure, the pressure at the liquid surface may be accurately calculated. However, unless the location of the liquid surface is known, such pressure determination cannot be made merely from the casing head pressure and the effect in height of the column of gas.

In my copending application Serial No. 171,170, I describe a sonic method of determining the location of this liquid level regardless of where the liquid level may be with respect to the location of the pump' and thus allow this simple method of determining the pressure to be performed. However, in some instances such pressure determination may be made by introducing gas into the well in suflicient quantities-to depress the normal liquid level down to the pump inlet and detecting when the liquid level arrives at the pump inlet. Thus, the location of the pump inlet being known, the calculations of casing head pressure necessary to maintain this liquid level at the pump inlet, plus the effect in height of the gas column between the pump inlet and the casing head, may be readily practiced. If the well is producing reasonable quantities of gas the same effect of depressing the liquid column to the pump inlet may be accomplished by merely closing of! the casing head and allowing the escaped gases to build up pressure until the column has beenso depressed.

As is recited in my copending application Serial No. 171,170, the pressure at the pump inlet may be plotted or calculated against the production rate of the pump for any two rates of production, either the static condition (zero production) and one 'rate of actual pumping of liquid from the well, or two different rates of actual production (actual pumping of liquid from the well), to provide a productivity index for that well from which the maximum production capacity'of that well may be determined.

anchors permit the successful creation and transmission of the peculiar wave patterns described hereinafter.

I have illustrated and described herein one simple method and apparatus by which the location of the liquid level at or adjacent the pump inlet may be readily determined as comprising a suitable pressure responsive receiving and trans-- lating mechanism coupled to the casing of the well in such manner that the pressure waves created at the pump when it takes in free gas may be detected and recorded. This apparatus is illustrated as including a pressure responsive microphone connected directly to the casing head 9 of the well as by means of coupling the same to the gas flow pipe I I so that variations in pressure existing within the well casing will impinge upon the microphone. This microphone may be of any desired type but I have illustrated herein a microphone and recording'apparatus corresponding to that described in detail in my copending application Serial No. 164,534, filed September 18, 1937, the microphone being of the condenser type and being coupled through a suitable amplifier and detector IS in such manner that the output of the amplifier may be connected to a galvanometer I I which operates to move a mirror id in accordance with the pressure impulses received by or impinging upon the microphone IS. The galvanometer. mirror l8 may be used to reflect a light beam l9 from a suitable source of light upon a screen 2| or recording tape or film, the path described by the light beam representing a translation of the pressure waves or sound waves generated at the pump. When the fluid surface is well above the pump, there will be observed a regular wavy pulsation of the light upon the screen or recording film but when the level of the fluid is so depressed that the pump takes in a quantity of free gas upon each stroke, a jerky motion is observed and a pattern will be described which repeats itself for each stroke of the pump. This repetition of similar wave patterns may be readily observed and distinguished from the normal pulsations or wave patterns described as a result of other disturbances; for example, one form of such repeated wave pattern is illustrated in Fig. 2 wherein it will be observed that a series of peaks are produced as indicated at A, B, C and D, these peaks repeated at regular I intervals, each'representing a stroke of the pump. It will be noted that the peaks A and B represent the pressure changes set up by the surging of the liquid level as the liquid is drawn into the pump while the relatively sharp break X between the peaks B and C represents the beginning of the entry of free gas into the pump, such entry of gas creating a wave of rarefaction which creates the peak 0. This same wave pattern is repeated at A, B, X, C and D and again at A", 3",

' distinct break X and the distinct wave of rareiaction C, a skilled operator may determine that such pattern is caused when the liquid is at or adjacent to the pump inlet. This wave pattern may be observed upon the screen 2| or may be recorded upon a tape recorder such as is commonly known in this art and one form of which is illustrated in my copending application Serial No. 164,534 hereinbefore referred to. It is also possible to employ an audible translating device by which this break in the wave pattern may be detected such as by employing a telephone re-' ceiver indicated at 22 coupled to the output circuit shown and described in my copending application Serial No. 164,534.

While in the specific embodiment of the invention illustrated herein, I haveshown a condenser type of microphone, it will be understood by those skilled in this art. that any other conventional microphone maybeemployed such as a hot-wire, ribbon or other type of microphone,

the characteristics of which will be afiected by changes in the pressure existing in pipe ll.

Having this means of knowing when the liquid level is at or near the pump the casing pressure is adjusted to maintain the liquid level a few feet above the pump inlet until the rate of production becomes constant under the increased casing pressure. From the casing pressure required to maintain the liquid level close to the pump the pressure at this level can be determined by adding to the casing head pressure the pressure on the liquid surface caused by the weight of the gas column above it (the liquid surface being at the pump inlet, its density may be disregarded in the calculations for production capacity) .casing head for the purpose of measuring the casing head pressure so that by observing this pressure gauge thepressures existing at the casing head when the liquid level is at or adjacent the pump entrance may be readily observed.

It will therefore be observed. that I have provided a ready and simple method by which pressure determinations and maximum production capacity determinations may be made upon a well without interrupting the production from the well and without requiring the necessity of removing any of the pump, Dump tubing or other apparatus which is employed in the production of the well.

While I have shown and described the preferred embodiment of my invention, I do not wish to be limited to any of the details illustrated or described herein except as defined in the appended claims.

I claim:

1. The method of determining when the sur-' face of the liquid in a well is at the level of a pump inlet, which comprises operating the pump to pump fluid from the well to thus cause surging of the liquid column in the well and pressure variations in the gas column in the well casing, and recording the wave form of the pressure variations in the gas at the casing head of the well to distinguish the smooth wave form produced when the liquid surface level is above the pump from the broken wave form resulting from the intake of free gas into the pump when the variations in the gas column in the well casing,

changing the casing head pressure to depress the liquid surface toward the level of the pump inlet,

recording the wave form of the pressure varia-' tions in the gas at the casing head to determine when the smooth wave form produced when the liquid surface level is above the pump changes to a broken wave form resulting from the intake of free gas into the pump when the liquid surface level is at the pump.

3. The method of determining when the surface of the liquid in a well is at the level of the pump inlet, which comprises operating the pump to pump liquid from the well to thus-cause surging of the liquid column in the well and pressure- 4. The method of determining when the sur-' face of the liquid in a producing well is'at the level of the pump inlet, which comprises; operating the pump to pump liquid from the well to thus cause surging of the liquid column in the well andpressure variations in the gas column in reproducing device to the gas column in the well casing to reproduce an observable pattern of the form of pressure waves produced in the gas coly umn, and observing the diiference in the form of the pressure waves produced in the why the surge of the liquid levelcaused by removal of liquid by the pump and those waves produced by 8 the entry of free gas in the pump.

5. The method of determining when the surface of the liquid in a producing well is at the level of the pump inlet, which comprises operating the pump to pump liquid from the well to 10 thus cause surging of the liquid column in the well and pressure variations in the gas column in the well casing, exposing a-microphone to the gas column in the well casing, and observing the difference in the effect upon the-microphone of i8 pressure waves created in the gas by the surge of the liquid level in the well caused by removal \of liquid by the pump and those waves produced by the entry of free gas in the pump.

6. .The method of determining when the surgo face of the liquid in a producing well is at the level of the pump inlet, which comprises operating the pump to pump liquid from the well to thus cause surging of the liquid column in the well and pressure variations in the gas column 25 in the well casing, exposing a diaphragm to the gas column in the well casing, and observing the difference in the movement in the diaphragm under pressure waves created in the gas by the surge of the liquid-level in the well caused by thewell casing, exposing a pressure wave form 80 removal 0! liquid by t e pump and those waves produced by the entry of free gas into the pump.

CRANFORD P. WALKER. 

